Modern medical science employs numerous electrically powered devices which are implanted in a living body. For example, such devices may be employed to deliver medications, to support blood circulation as in a cardiac pacemaker or artificial heart, and the like. Many implantable devices contain batteries which may be rechargeable by transcutaneous induction of electromagnetic fields in implanted coils connected to the batteries. Transcutaneous inductive recharging of batteries in implanted devices is disclosed for example in U.S. Pat. No. 3,923,060; U.S. Pat. No. 4,082,097; U.S. Pat. No. 4,143,661; U.S. Pat. No. 4,665,896; U.S. Pat. No. 5,279,292; U.S. Pat. No. 5,314,453; U.S. Pat. No. 5,372,605, and many others.
Other methods for recharging implanted batteries have also been attempted. For example, U.S. Pat. No. 4,432,363 discloses use of light or heat to power a solar battery within an implanted device. U.S. Pat. No. 4,661,107 discloses recharging of a pacemaker battery using mechanical energy created by motion of an implanted heart valve.
A number of implanted devices have been powered without batteries. U.S. Pat. No. 3,486,506 and U.S. Pat. No. 3,554,199 disclose generation of electric pulses in an implanted device by movement of a rotor in response to the patient's heartbeat. U.S. Pat. No. 3,563,245 discloses a miniaturized power supply unit which employs mechanical energy of heart muscle contractions to generate electrical energy for a pacemaker. U.S. Pat. No. 3,456,134 discloses a piezoelectric converter for electronic implants in which a piezoelectric crystal is in the form of a weighted cantilever beam capable of responding to body movement to generate electric pulses. U.S. Pat. No. 3,659,615 also discloses a piezoelectric converter which reacts to muscular movement in the area of implantation. U.S. Pat. No. 4,453,537 discloses a pressure actuated artificial heart powered by a second implanted device attached to a body muscle which in turn is stimulated by an electric signal generated by a pacemaker.
In spite of all these efforts, a need remains for efficient generation of energy to supply electrically powered implanted devices.